It has been conventional to produce sandwich panels using a mineral wool core which is sandwiched between and bonded to rigid or semi-rigid sheet material skins, often formed of aluminium. It has also been known to cut slabs of mineral wool fibers which have been compacted and treated with a binder into strips having a width corresponding to the desired distance between the facing skins and to turn the strips through 90.degree. before bonding to the skins. In this manner, it is possible for the direction of the fibers, which run generally parallel to the length of the strips, to extend in a direction generally transverse to the planes of the skins, which greatly improves the resistance against separation of the core due to forces acting on the skins.
Since mineral wool slabs are traditionally only produced in limited lengths of say 1 to 1.2 meters, there is a need in panels which have a greater dimension than the length dimension of the core strips, to use more than one length of strip in end-to-end relation.
It has been found, when one is using thin skin material in particular, that the transverse divisions resulting from the abutting ends of the strips show through the skins in the finished panel.